Pure manganese crystal intergrowths



Patented Mar. 6, 1952 This invention relates to pure manganese crystal intergrowths. Pure manganese has heretofore only been prepared by distillation. The sublimation procedure first used by Gayler produced the high temperature gamma form of manganese which on cooling transformed to the room temperature stable alpha form with internal cracking and production of large surface.

The distillation procedure is not commercially practicable and the product is not satisfactory as an alloying metal because of its fragility and large surface. Manganese of moderate purity has been produced by aqueous electrolysis and is an article of commerce, however such manganese contains substantial amounts of both oxygen and hydrogen.

Manganese has been produced by fusion electrolysis using fluoride baths but the product has been impure. Crystals were produced by Aten Hertog and Westenberg using a molten chloride bath at 660 and hence producing manganese in the alpha form. Since no precautions to eliminate oxygen were taken the crystals were certainly impure.

I have found that by carrying out the electrorefining of manganese in a temperature range in which the beta form of manganese is stable namely 750-900 C., and in a molten bath free from oxygen, that pure oxygen-free coarse idiomorphic crystal intergrowths of beta manganese are formed. Such coarse crystal intergrowths are retained in outer form without fracturing when cooled to room temperature and are more satisfactory as an alloying material than transformed gamma manganese or the porous hydrogen and oxygen containing cathode chips of electrolytic manganese currently marketed.

A preferred bath for carrying out my invention is composed of sodium chloride having dissolved therein from 110% of manganese as chloride. I have found that the crystal intergrowths obtained from this electrolyte are purer and larger when analysis indicates a small amount of dissolved sodium and a lower valence of manganese in the electrolyte. I determine these by solution of the electrolyte in acidified ferric sulphate; hydrogen evolved indicates dissolved sodium and reduction of the ferric sulphate indicates a lower valence of manganese. The bath may be prepared by mixing the truly anhydrous chlorides and preferably adding a little metallic sodium. A convenient and preferred method of preparing the electrolyte is to start with an electrolyte for refining titanium as set forth in US. Patent 2,817,631 that is, an electrolyte of molten NaCl in which is dissolved 27% titanium as lower chlorides and 1-3% sodium. Manganese metal is made an anode in this electrolyte and an inert iron cathode provided electrolysis is carried out at a cathode current density of 600 amperes per square foot unitl the bath is free from titanium. The bath will then be found to contain 1-7% manganese as chloride. It will show a significant evolution of hydrogen in acidified ferric sulphate and a reducing power to ferric sulphate of at least .1 ml. of tenth normal dichromate per gram of salt bath. This bath is then used to refine impure manganese such as ferromanganese.

The temperature of the bath during such refining is BOO-850 C. The bath is maintained in an atmosphere of pure argon or helium and the product cooled in such an inert atmosphere. Cathode current density is 100- 1000 amperes per square foot and the product as formed consists of coarse idiomorphic crystal intergrowths of beta manganese. These idiomorphic crystal intergrowths after washing with a solution of K C O rinsing thoroughly and drying, showed on analysis less than .01% total impurities.

l have found that the anode material for refining must contain manganese as metal or carbide. Impurities more noble than manganese are not transferred from anode material to cathode product. Ordinary standard ferromanganese is a satisfactory anode material when comminuted to /s inch. Ferromanganese containing only 30-50% manganese is also a satisfactory anode material.

Example I In this example I start with an electrolytic bath for titanium refining containing sodium chloride having dissolved therein 4.5% soluble titanium as chloride with an average valence of 2.4 and dissolved metallic sodium of 1%. I maintain this bath at 850 C. in an argon atmosphere and provide an inert cathode and an anode material in an iron basket surrounding the cathode of standard ferromanganese containing about manganese-7% carbon13% iron. I pass a direct current through the cell and remove the cathode product from time to time until it shows on analysis no titanium. The bath then analyzed 4% manganese and a significant amount of sodium (dissolved metallic). I then replace the cathode and continue to pass current. For every ampere hour passed approximately l.l grams of manganese is deposited adherent to the cathode in the form of idiomorphic crystal intergrowths having the outer form of beta manganese. When removed from the cell without exposure to air, washed in water, rinsed with K C O solution, rinsed with water and vacuum driedthese crystal intergrowths analyzed 99.99 plus manganese and less than .01% of oxygen and hydrogen taken together.

Example II In this example I provide a bath of anhydrous sodium chloride and manganese chloride containing 8% manganese. ample I and proceed in the same way to refine a crude ferromanganese containing 40% manganese-50% iron- 5% carbon-2% silicon-3% other impurities including copper and nickel. The product was identical with that of Example I.

What is claimed is:

As an article of manufacture idiomorphic crystal intergrowths, uncontaminated by any material on which they may have been formed, of pure manganese in outward form of the beta modification said crystal intergrowths being at least 0.1 mm. in maximum dimension and containing, as formed, not more than 0.01% impurity of the group consisting of oxygen and hydrogen.

References Cited in the file of this patent UNITED STATES PATENTS 1,815,054 Driggs July 21, 1931 2,398,589 Mitchell Apr. 16, 1946 2,656,595 Stern et al. Oct. 27, 1953 2,678,879 Nuesch May 18, 1954 2,752,299 Cooper June 26, 1956 2,752,303 Cooper June 26, 1956 2,817,631 Gullett Dec. 24, 1957 OTHER REFERENCES lz tetallurgy of the Rarer Metals-Manganese, pages -136, edited by Sully, published in 1955.

I place this electrolyte in a cell like that of EX 

